1. Field of the Invention
The present invention relates to a lens driving device mounted in the camera of a mobile phone, in particular to a lens driving device with an automatic focusing function and capable of enabling a lens to move in the direction of an optical axis.
2. Description of Related Art
FIG. 5 illustrates a section view illustrating a lens driving device 20 based on a representative existing electromagnetic driving mechanism disclosed by Patent Document 1 (JP 2004-280031), FIG. 6A is an exploded view, and FIG. 6B is an enlarged view of a main part of the lens driving device.
As shown in each figure, the lens driving device 20 includes a box body 21, a lens support 22, a magnet yoke 23, a coil 24, a permanent magnet assembly 25, a front side spring component 26A and a rear side spring component 26B. When the direction of the optical axis of an unshown lens is taken as a direction of Z axis, the lens support 22 of the lens driving device 20 for retaining the lens can move along the direction of Z axis.
The magnet yoke 23 is made of soft magnetic material, and includes an outer peripheral wall 23a, an inner peripheral wall 23b and a top wall part 23c for connecting the outer peripheral wall 23a with the inner peripheral wall 23b together at the +Z side. The magnet yoke 23 has an approximately n-shaped transverse cross section, and is mounted in the box body 21. The permanent magnet assembly 25 is circular arc column-shaped, and includes several circular arc magnets arranged in a circular column. The circular arc magnets are cylindrically mounted on the inner side of the outer peripheral wall 23a of the magnet yoke 23.
The coil 24 is wound around an axis parallel to the Z axis, and disposed between the permanent magnet assembly 25 and the inner peripheral wall 23b of the magnet yoke 23. That is, the coil 24, the permanent magnet assembly 25 and the inner peripheral wall 23b are encircled one inside another in the radial direction, and are respectively separated at an interval. The coil 24 is fixed on the +Z side face of a flange part 22a of the lens support 22. The flange part 22a of the lens support 22 enters the −Z side of the inner peripheral wall 23b of the magnet yoke 23. The coil 24 can move along the direction of Z axis in a space defined by the inner peripheral wall 23b, the top wall part 23c of the magnet yoke 23 and the permanent magnet assembly 25.
The box body 21 includes four outer side support columns 21a vertically arranged on the outer side of the outer peripheral wall 23a of the magnet yoke 23 and a base part 21b positioned at the rear (on the −Z side) of the lens support 22. The magnet yoke 23 is fixed on the +Z side of the base part 21b of the box body 21.
The lens support 22 is formed to be in the shape of a cylinder capable of accommodating the unshown lens inside. The lens support 22 is mounted to be capable of freely moving along the optical axis on the inner peripheral side of the magnet yoke 23.
The front side spring component 26A and the rear side spring component 26B are both plate springs made of alloy materials with good electrical conductivity. The front side spring component 26A is formed to be annular, and is disposed in the front (on the +Z side) of the lens support 22 in the direction of the optical axis. The rear side spring component 26B includes a +Y side circular arc spring component 26C and a −Y side circular arc spring component 26D which are circular arc shapes and form a circle together, and is disposed at the rear (on the −Z side) of the lens support 22 in the direction of the optical axis.
Each of the front side spring component 26A and the rear side spring component 26B includes an inner side retaining part 26a connected with the side of the lens support 22, an outer side retaining part 26b connected with the side of the box body 21, a plurality of wrist parts 26c disposed between the inner side retaining part 26a and the outer side retaining part 26b and extending along the circumference direction, a plurality of inner side connecting parts 26m for connecting the inner side retaining part 26a with one ends of the wrist parts 26c, and a plurality of outer side connecting parts 26n for connecting the outer side retaining part 26b with the other ends of the wrist parts 26c. 
Moreover, the rear side spring component 26B is provided with two power supply terminals 26d connected with an external power supply as a power supply path.
The inner side retaining part 26a of the front side spring component 26A is connected with the connecting surface 22c on the +Z side of the lens support 22. The inner side retaining part 26a of the rear side spring component 26B is connected onto −Z side face of the flange part 22a of the lens support 22.
The outer side retaining part 26b of the front side spring component 26A is connected onto the +Z side face of the top wall part 23c of the magnet yoke 23. The outer side retaining part 26b of the rear side spring component 26B is connected onto the +Z side face of the base part 21b of the box body 21.
The end part 22b on the −Z side of the lens support 22 abuts against the base part 21b of the box body 21. By taking the (offset) states of the inner side retaining parts 26a of the front side spring component 26A and the rear side spring component 26B closer to the +Z side than the outer side retaining parts 26b of the front side spring component 26A and the rear side spring component 26B as initial positions, the front side spring component 26A and the rear side spring component 26B are respectively subjected to application force in the −Z direction by restoring force generated by the wrist parts 26c of the front side spring component 26A and the rear side spring component 26B.
The winding terminal 24a of the coil 24 is connected with the inner side retaining part 26a of the +Y side circular arc spring component 26C through tin soldering or spot welding. Moreover, the winding terminal 24b of the coil 24 is connected with the inner side retaining part 26a of the −Y side circular arc spring component 26D through tin soldering or spot welding.
Thus, the lens support 22 of the lens driving device 20 is subjected to acting force in the direction of −Z axis applied by restoring force generated by the wrist parts 26c of the front side spring component 26A and the rear side spring component 26B. Moreover, when the power supply terminals 26d are powered, and a current is flowing in the coil 24, a driving force is generated in the direction of +Z axis and is greater than the restoring force of the wrist parts 26c, the end part 22b on the −Z side of the lens support 22 leaves away from the base part 21b and floats up in the +Z direction.
As shown in FIG. 6B, under the condition that the winding terminals 24a, 24b of the coil 24 are connected to the inner side retaining part 26a of the rear side spring component 26B through tin soldering, tin soldering fluxes 27 contained in a tin soldering material are scattered towards the tin soldering part and are attached onto peripheral components (the lens support 22, the rear side spring component 26B and the like), or annealing can be generated for the rear side spring component 26B heated by tin soldering iron or spot welding.
Thus, when the tin soldering fluxes 27 are attached onto the lens support 22 or the rear side spring component 26B, the tin soldering fluxes can also exist in a gap between the lens support 22 and the rear side spring component 26B, a gap between the lens support 22 and the base part 21b of the box body 21, a gap between the rear side spring component 26B and the base part 21b, and the like. In such condition, even if the coil 24 is electrified, the lens support 22 may be adhered by the tin soldering fluxes and resist to Lorentz force generated by the electrified coil 24, and keeps still all the time and cannot move to a distance corresponding to the energizing amount. On the other hand, the lens support 22 may suddenly move possibly due to sudden falling of the soldering fluxes 27 so as to cause movement disorders, and the lens support 22 can not generate linear movement corresponding to power supply either.
Moreover, under the condition that the inner side retaining part 26a of the rear side spring component 26B is subjected to pressing force applied by a soldering iron sharp or a welding head of the tin soldering iron, the rear side spring component 26B may be deformed plastically sometimes. Specifically, when the pressing force generated by the soldering iron sharp of the tin soldering iron or the welding head through spot welding is applied to the inner side retaining part 26a, the rear side spring component 26B is plastically deformed, and the lens support 22 is possibly suspended at an inclined state. And then, when the rear side spring component 26B is heated by the tin soldering iron or the welding head for annealing, the elastic force of the rear side spring component 26B changes to cause that the spring coefficient of the spring component 26 changes, but that the action sensitiveness at that time may be offset with a preset value is also taken into consideration.